Laser system delivering ultra-short pulses along multiple beam delivery paths

ABSTRACT

A laser system includes a laser source generating a laser beam having ultra-short pulses; a laser delivery assembly optically receiving the laser beam and comprising: a beam splitter configured to split the laser beam between a first beam delivery path and a second beam delivery path; and at least one focusing lens optically coupled to the beam splitter and configured to focus the laser beam from each of the first beam delivery path and the second beam delivery path to a focal point on a predefined plane; wherein the first beam delivery path intersects the predefined plane at a first angle, the second beam delivery path intersects the predefined plane at a second angle, and a first pulse from the first beam delivery path and a second pulse from the second beam delivery path are coincident at the focal point.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 62/728,927, filed Sep. 10, 2018, the entirety ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Lasers which generate ultra-short pulses have found numerousapplications across a wide variety of industries, including bothindustrial manufacturing applications to medical applications, amongothers. Current technologies utilize ablative lasers (e.g., CO2 orEr:YAG) to provide localized destruction of substrate materials. In themedical field, these substrate materials are generally soft tissues, andablation of the tissues is used to promote skin remodeling and healing.This technique has been shown to be beneficial in skin rejuvenation,aesthetic improvement of the skin, treatment of hypertrophic scars,removal of unwanted pigments and/or skin lesions, to assist in drugdelivery, and for oncological treatment. One potential drawback of theselaser treatments is that they often result in destruction of all layersof the skin until the desired treatment depth is achieved. This resultsin epidermal destruction and an inability to target specific layers ofthe skin and underlying tissues without injury to the more superficiallayers.

Multiphoton technologies utilize non-linear photonic absorption toexcite molecules, particularly for microscopy purposes. Utilizing themultiphoton concept, a target is excited utilizing two or more photons,each having a lower energy (and subsequently longer wavelengths) thanstandard energies needed to cause non-linear excitement. Energies fromthe multiple photons are concentrated at the focal point of the lenssuch that the probability of this non-linear excitement is extremely lowexcept at the focal point. Utilizing a high flux of photons provided bya laser that generates ultra-short pulses and near-infrared to infraredemissions, such as a femtosecond laser, the density of photons may beincreased at the desired focal depth while also reducing the probabilityof damaging surface layers of the tissue and other subsurface layersthat reside above the targeted layer. Therefore, excitation occursprimarily at the desired depth with little scatter and good penetrationdepth secondary to the use of longer wavelengths (i.e., near infra-red).While these technologies have been utilized for imaging of 3D tissues,there has been limited clinical application of these technologies forthe treatment of the skin and deeper tissues. Part of the reason forthis is that such treatments require increased energy, which in turnincreases the probability of tissue damage to the layers of tissue abovethat layer being treated.

SUMMARY OF THE INVENTION

Exemplary embodiments according to the present disclosure are directedto a laser system which generates ultra-short pulses to make sub-surfacemodifications in a targeted layer of a substrate while alsosubstantially reducing the probability that layers of substrate abovethe targeted layer will not be damaged during the process. In themedical field, the substrate may be skin, subcutaneous tissues, fat, andblood vessels, among other types of tissues. Specifically, the lasersystem may include tuneable optics which enable greater control ofablative energies only to targeted sub-surface tissues and not tooverlying or underlying tissues. This allows for treatment of individuallayers of tissue without damage to adjacent tissues.

In one separate aspect, the invention may be a laser system including: alaser source generating a laser beam including ultra-short pulses; alaser delivery assembly optically coupled to the laser source to receivethe laser beam, the laser delivery assembly including: a beam splitterconfigured to split the laser beam between a first beam delivery pathand a second beam delivery path; and at least one focusing lensoptically coupled to the beam splitter and configured to focus the laserbeam from each of the first beam delivery path and the second beamdelivery path to a focal point on a predefined plane; wherein the firstbeam delivery path intersects the predefined plane at a first angle, thesecond beam delivery path intersects the predefined plane at a secondangle, and a first pulse from the first beam delivery path and a secondpulse from the second beam delivery path are coincident at the focalpoint.

In another aspect, the invention may be a method of modifying asubstrate, the method including: generating a laser beam includingultra-short pulses; splitting the laser beam between a first beamdelivery path and a second beam delivery path; focusing the laser beamfrom each of the first beam delivery path and the second beam deliverypath to a focal point on a predefined plane within the substrate, thefirst beam delivery path intersecting the predefined plane at a firstangle, and the second beam delivery path intersecting the predefinedplane at a second angle; and wherein a first pulse from the first beamdelivery path and a second pulse from the second beam delivery path arecoincident at the focal point.

In still another aspect, the invention may be a laser system including:a laser source generating a laser beam including femtosecond pulses; alaser delivery assembly optically coupled to the laser source to receivethe laser beam, the laser delivery assembly including: a beam splitterconfigured to split the laser beam between a first beam delivery pathand a second beam delivery path; a first focusing lens optically coupledto the beam splitter and positioned within the first beam delivery path,the first focusing lens configured to focus the laser beam from thefirst beam delivery path to a focal point on a predefined plane; asecond focusing lens optically coupled to the beam splitter andpositioned within the second beam delivery path, the second focusinglens configured to focus the laser beam from the second beam deliverypath to the focal point on the predefined plane; wherein the first beamdelivery path intersects the predefined plane at a first angle, thesecond beam delivery path intersects the predefined plane at a secondangle, and a first pulse from the first beam delivery path and a secondpulse from the second beam delivery path are coincident at the focalpoint.

In yet another aspect, the invention may be a method of modifying asubstrate, the method including: generating a laser beam includingfemtosecond pulses; splitting the laser beam between a first beamdelivery path and a second beam delivery path; focusing the laser beamfrom the first beam delivery path to a focal point on a predefined planewithin a substrate using a first focusing lens disposed in the firstbeam delivery path, the first beam delivery path intersecting thepredefined plane at a first angle; focusing the laser beam from thesecond beam delivery path to the focal point on the predefined planeusing a second focusing lens disposed in the second beam delivery path,the second beam delivery path intersecting the predefined plane at asecond angle; and wherein a first pulse from the first beam deliverypath and a second pulse from the second beam delivery path arecoincident at the focal point.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe exemplary embodiments, will be better understood when read inconjunction with the appended drawings. It should be understood,however, that the invention is not limited to the precise arrangementsand instrumentalities shown in the following figures:

FIG. 1 is schematic illustration of a first embodiment of a laser systemwhich delivers ultra-short pulses along multiple beam delivery paths.

FIG. 2 is schematic illustration of a second embodiment of a lasersystem which delivers ultra-short pulses along multiple beam deliverypaths.

FIG. 3 is schematic illustration of a third embodiment of a laser systemwhich delivers ultra-short pulses along multiple beam delivery paths.

FIG. 4 is a flowchart illustrating operation of a laser system whichdelivers ulta-short pulses along multiple beam delivery paths.

DETAILED DESCRIPTION OF THE INVENTION

The description of illustrative embodiments according to principles ofthe present invention is intended to be read in connection with theaccompanying drawings, which are to be considered part of the entirewritten description. In the description of embodiments of the inventiondisclosed herein, any reference to direction or orientation is merelyintended for convenience of description and is not intended in any wayto limit the scope of the present invention. Relative terms such as“lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,”“down,” “left,” “right,” “top” and “bottom” as well as derivativesthereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should beconstrued to refer to the orientation as then described or as shown inthe drawing under discussion. These relative terms are for convenienceof description only and do not require that the apparatus be constructedor operated in a particular orientation unless explicitly indicated assuch. Terms such as “attached,” “affixed,” “connected,” “coupled,”“interconnected,” and similar refer to a relationship wherein structuresare secured or attached to one another either directly or indirectlythrough intervening structures, as well as both movable or rigidattachments or relationships, unless expressly described otherwise.Moreover, the features and benefits of the invention are illustrated byreference to the preferred embodiments. Accordingly, the invention isnot be limited to such preferred embodiments illustrating some possiblenon-limiting combinations of features that may exist alone or in othercombinations of features; the scope of the invention therefore shouldnot be limited unless otherwise expressly stated in the claims appendedhereto.

In the context of the embodiments described herein, optics and opticalsystems are disclosed which include one or more optical elements. It isto be understood that various ones of the optical elements could bereplaced by a plurality of other optical elements which provide the samefunctionality. Further, other optical elements could be included as partof the optical systems described herein in order to provide additionalfunctionality beyond that which is expressly disclosed or describedherein. The scope of the claims are not to be limited unless otherwiseexpressly stated therein.

Turning in detail to the drawings, FIG. 1 illustrates a laser system 11which includes a laser source 13 configured to generate a laser beam.The laser beam is formed by a plurality of ultra-short pulses 15 and isdirected by a plurality of optical elements, which are discussed indetail below, toward and into a substrate 17. An ultra-short laser pulseis one that has a duration of between about 30 picoseconds and about 1femtosecond. Advantageously, ultra-short laser pulses may be used toproduce multiphoton excitation events within the substrate 17. Throughsuch multiphoton excitation events, which are the result of interactionsbetween the ultra-short pulses 15 of the laser beam and the matterforming the substrate 17, the substrate 17 can be modified by the laserbeam through what is known as ablation. Depending upon the substrate 17and the intent of the operator of the laser system 11, in certainembodiments the modification may result in microstructures being formedin the substrate 17. In embodiments in which the substrate 17 is atissue, whether the tissue is in vivo or in vitro, the modification maybe elimination of a feature of the tissue, a cutting of a feature of thetissue, a separating of two features of the tissue, or any othermodification that may serve a medical purpose for in vivo tissue in thedetermination of an attending physician or a research purpose for invitro tissue in the determination of a researcher.

The laser beam is directed along a primary beam path 19, in which otheroptical elements of the laser system 11 are positioned to interact withthe laser beam. In certain embodiments, the laser source 13 may be afemtosecond laser. In certain embodiments, the laser source 13 maygenerate the laser beam in the infrared to near-infrared wavelengths.For example, in certain embodiments the laser source 13 may be atitanium sapphire laser. In general, the longer wavelength of light inthe infrared and near-infrared wavelengths results in greater tissuepenetration with less scatter. In still other embodiments, the lasersource 13 may generate the laser beam in any other spectrum that isappropriate to create a multiphoton excitation event within a targetsubstrate or within a specific layer of a target substrate. In certainembodiments, the laser source 13 may be a tunable pulsed laser source.Such tunable pulsed laser sources are well known to those of ordinaryskill in the art of ultra-short pulsed lasers.

From the laser source 13, the laser beam is directed along the primarybeam path 19 to beam/pulse shaping optics 21, which may be used tomanipulate the temporal profile of the ultra-short laser pulses. Forexample, the ultra-short laser pulses may undergo pulse shaping which isused to shorten or elongate the duration of the ultra-short pulses 15,or to generate complex pulse profiles. Depending upon the form of theultra-short pulses 15 produced by the laser source 13 and theapplication for which the laser system 11 is being used, in certainembodiments the beam/pulse shaping optics 21 may be omitted from thelaser system 11. In certain embodiments, the laser beam may pass throughany number of lenses, polarizers, splitters, mirrors, and/or fibersafter being generated by the laser source and before entering thesubstrate. Such additional optical elements, although they may bepresent in certain embodiments, are not to be limiting of the inventionunless expressly recited in the claims.

Following the beam/pulse shaping optics 21, the laser beam is directedthrough a dichroic mirror 23. The dichroic mirror 23 is constructed toallow the laser beam, at the generated wavelength, to pass throughunaltered. The dichroic mirror 23, does however reflect light returningin the opposite direction down the beam path, i.e., the directionstarting at the substrate 17 along the beam path toward to the lasersource 13, that is emitted from excitation events. Any such emittedfeedback light is directed by the dichroic mirror 23 into the detector25 so that the excitation events may be detected and analyzed asappropriate.

After passing through the dichroic mirror 23, the laser beam is directedto the laser delivery assembly 31, within which the laser beam isincident upon a beam splitter 33. The beam splitter 33 splits theprimary beam path 19 into a first beam delivery path 35 and a secondbeam delivery path 37. The laser beam is thus also divided between thefirst beam delivery path 35 and the second beam delivery path 37. Bydividing the laser beam between the first and second beam delivery paths35, 37, the power of the pulses traveling along each path is less thanthe power of each pulse traveling along the primary beam path 19. Byappropriate selection of the beam splitter 33, the power of each pulsefrom the primary beam path 19 can be approximately divided in halfbetween the first and second beam delivery paths 35, 37.

As shown, the beam splitter 33 uses reflection to split the laser beambetween the first and second beam delivery paths 35, 37. In certainembodiments, the beam splitter 33 may instead use refraction to splitthe laser beam between the first and second beam delivery paths 35, 37.One such example of a refractive beam splitter is a grating. Other typesof reflective and/or refractive beam splitters may also be used.

From the point that the laser beam is separated by the beam splitter 33to the focal point 51 within the substrate 17, the power of each pulsetraveling along each of the first and second beam delivery paths 35, 37is reduced such that the ultra-short pulses with reduced energy do nothave sufficient power to cause a multiphoton excitation event within thesubstrate 17. Instead, a multiphoton excitation event may only be causedwhen the energies from pulses propagating along each of the first andsecond beam delivery paths 35, 37 are recombined when coincident at thefocal point 51 within the substrate 17.

In order to achieve the desired coincidence at the focal point 51, theoptical path length of the first and second beam delivery paths 35, 37,between the point of incidence of the primary beam path 19 with the beamsplitter 33 and the focal point 51, should be the same. As shown in FIG.1, the first beam delivery path 35 is has an optical path length that isshorter than the optical path length of the second beam delivery path37. To compensate for this difference in optical path lengths, a timedelay optical element 39 is placed within the first beam delivery path35. This time delay optical element 39 serves to slow down pulsestraveling along the first beam delivery path 35 so that the effectiveoptical path length of the first beam delivery path 35 is the same asthe optical path length of the second beam delivery path 37. In certainembodiments, the time delay optical element 39 is a plate of glasshaving an index of refraction that is greater than the index ofrefraction of atmosphere, to slow down the pulses in the first beamdelivery path 35, and a thickness that is sufficient to introduce thedesired delay. In certain embodiments, the beam splitter 33 can alsoperform the function of providing the desired time delay by selection ofa beam splitter with a width sufficient to introduce the desired delay.

A first focusing lens 55 is in the first beam delivery path 35 andpositioned to focus the laser beam from the first beam delivery path 35to the focal point 51. The focal point 51 lies within a predefined plane53 that extends through the substrate 17. In FIG. 1, the laser beam fromthe first beam delivery path 35 is normal to the predefined plane 53,such that the angle α between the laser beam from the first beamdelivery path 35 and the predefined plane 53 is fixed at 90°. Thus, forthe laser beam from the first beam delivery path 35 of this embodiment,the predefined plane 53 is also the focal plane of the first focusinglens 55.

A mirror 57 and a second focusing lens 59 are in the second beamdelivery path 37. The mirror 57 is optically positioned to direct thelaser beam reflected from the beam splitter 33 along the second beamdelivery path 37 to the second focusing lens 59, and the second focusinglens 59 is positioned to focus the laser beam from the second beamdelivery path 37 to the focal point 51, such that the laser beam fromboth the first and second beam delivery paths 35, 37 are coincident atthe focal point 51. In FIG. 1, the laser beam from the second beamdelivery path 37 is at an acute angle β with respect to the predefinedplane 53. Thus, in this embodiment, the angle β between the laser beamfrom the second beam delivery path 37 with respect to the predefinedplane 53 is less than the angle α between the laser beam from the firstbeam delivery path 35 and the predefined plane 53.

The laser system 11 includes a positioning assembly, which forsimplicity in FIG. 1 is depicted by the support structures 63, 65, 67.Although not shown explicitly, it should be understood that thepositioning assembly, including the support structures 63, 65, 67, alsoincludes one or more servo motors or other rotary/linear actuators,electronics, and other components which enable the positioning assemblyto move the various optical components as shown and described. Suchmechanical positioning assemblies are well known to those of skill inthe art of rotary and linear actuator systems. The positioning assembly,through the support structures 63, 65, 67, is configured to move thefirst and second focusing lenses 55, 59 and the mirror 57. In certainembodiments, the mirror 57 and the support structure 65 may be a singleunit in the form of a steering mirror. In certain of these embodiments,a fast steering mirror may be used for the mirror 57 and the supportstructure 65.

The laser system 11 also includes a controller 71 which is operablycoupled to the laser source 13, the detector 25, and each of the supportstructures 63, 65, 67 through control lines to enable full control ofthe laser system 11, including positioning of the focal point 51 andoperation of the laser source 13 so that the substrate 17 can bemodified. The controller 71 enables simultaneous control over each ofthe support structures 63, 65, 67 to ensure that the laser beam fromboth the first and second beam delivery paths 35, 37 coincide at thefocal point 51. In certain embodiments, the controller 71 may bepre-programmed to perform a desired modification to the substrate 17 sothat the modification process can be automated. In certain otherembodiments, the controller 71 may be operated by a user to enablecontrol of the modification process in real time.

The support structure 63 supports the first focusing lens 55 and enablestranslation of the first focusing lens 55 toward and away from thesubstrate. Translation of the first focusing lens 55 toward thesubstrate moves the focal point 51, and also the predefined plane 53,deeper into the substrate 17. Similarly, translation of the firstfocusing lens 55 away from the substrate moves the focal point 51, andthus also the predefined plane 53, toward the surface of the substrate17.

The support structure 65 supports the mirror 57 and enables rotation ofthe mirror 57 about a central point of the reflective surface of themirror 57. The support structure 67 supports the second focusing lens 59and enables translation of the second focusing lens 59 in twodirections, the first direction being toward and away from the substratealong an optical axis of the second focusing lens 59, and the seconddirection being orthogonal to the first direction. The support structure67 also enables rotation of the second focusing lens 59 about one ormore axes orthogonal to the optical axis of the second focusing lens 59.In combination, by being able to rotate the mirror 57 and independentlyrotate and translate the second focusing lens 59, the laser beam fromthe second beam delivery path 37 may be brought to focus at the focalpoint 51, so that the laser beam from each of the first and second beamdelivery paths 35, 37 coincide at the focal point 51.

In certain embodiments, the laser delivery assembly 61 and the supportstructures 63, 65, 67 may be incorporated into a handheld device. Insuch an embodiment, the controller 71 may control the depth of the focalpoint 51 within the substrate, while the user manually controls lateralmovement of the focal point 51 within the predefined plane 53.Alternatively, in such an embodiment the user may operate the controllerto set the focal point 51 at a fixed distance from the support structure63, thereby requiring the user to manually control the depth of thefocal point 51 within the substrate 17 while also manually controllinglateral movement of the focal point 51 within the predefined plane 53.

In the embodiment shown, the beam delivery paths 35, 37 are shown ashaving different optical path lengths. In certain embodiments, arefractive beam splitter may be employed, instead of the reflective beamsplitter shown, in lieu of introducing a time delay into one of the beamdelivery paths. In certain other embodiments, additional opticalelements may be introduced into the shorter of the two paths so that thebeam delivery paths 35, 37 have the same optical path length.

In certain embodiments of the laser delivery assembly 31, additionalbeam delivery paths may be added by placement of the appropriate opticalcomponents. Any such additional beam delivery paths that are introducedinto the laser delivery assembly 31 may use any of the beam steering andbeam focusing techniques expressly or impliedly disclosed herein. Suchadditional delivery paths may have the same or different optical pathlengths as compared to the beam delivery paths 35, 37.

FIG. 2 illustrates another embodiment of a laser system 111 which may beused to modify a substrate 17. The laser system 111 includes a lasersource 13 configured to generate a laser beam formed by a plurality ofultra-short pulses 15, and the laser beam is directed toward and intothe substrate 17. In certain embodiments, the laser source 13 may be afemtosecond laser. In certain embodiments, the laser source 13 maygenerate the laser beam in the infrared to near-infrared wavelengths. Incertain embodiments, the laser source 13 may be a tunable pulsed lasersource.

The laser beam is directed along a primary beam path 19, in which otheroptical elements of the laser system 111 are positioned to interact withthe laser beam. From the laser source 13, the laser beam is directedalong the primary beam path 19 to beam/pulse shaping optics 21, whichmay be used to manipulate the temporal profile of the ultra-short laserpulses. Again, depending upon the form of the ultra-short pulses 15produced by the laser source 13 and the application for which the lasersystem 111 is being used, in certain embodiments the beam/pulse shapingoptics 21 may be omitted from the laser system 111. In certainembodiments, the laser beam may pass through any number of lenses,polarizers, splitters, mirrors, and/or fibers after being generated bythe laser source and before entering the substrate. Such additionaloptical elements, although they may be present in certain embodiments,are not to be limiting of the invention unless expressly recited in theclaims.

Following the beam/pulse shaping optics 21, the laser beam is directedthrough a dichroic mirror 23, which allows the laser beam to passthrough and directs light emitted from excitation events into thedetector for feedback and analysis.

After passing through the dichroic mirror 23, the laser beam is directedto the laser delivery assembly 131, within which the laser beam isincident upon the beam splitter 133. The beam splitter 133 splits theprimary beam path 19 into a first beam delivery path 135 and a secondbeam delivery path 137. The laser beam is thus also divided between thefirst beam delivery path 135 and the second beam delivery path 137, inthe same manner as previously described.

As shown, the beam splitter 133 uses reflection to split the laser beambetween the first and second beam delivery paths 135, 137. In certainembodiments, other types of reflective and/or refractive beam splittersmay also be used.

In order to achieve the desired coincidence at the focal point 51, theoptical path length of the first and second beam delivery paths 135,137, between the point of incidence of the primary beam path 19 with thebeam splitter 133 and the focal point 51, should be the same. Asdiscussed above, a time delay optical element may be incorporated intothe laser delivery assembly 131 as needed.

A first mirror 139 is in the first beam delivery path 135 immediatelyfollowing the beam splitter 133. This first mirror 139 is in a fixedposition and directs the laser beam along the first beam delivery path135 to a second mirror 141, which in turn directs the laser beam alongthe first beam delivery path 135 to a first focusing lens 143. The firstfocusing lens 143 is positioned to focus the laser beam from the firstbeam delivery path 135 to the focal point 51. In FIG. 2, the laser beamfrom the first beam delivery path 135 is at an acute angle α withrespect to the normal 145 of the predefined plane 53.

A third mirror 147 and a second focusing lens 149 are in the second beamdelivery path 137. The third mirror 147 is optically positioned todirect the laser beam reflected from the beam splitter 133 along thesecond beam delivery path 137 to the second focusing lens 149, and thesecond focusing lens 149 is positioned to focus the laser beam from thesecond beam delivery path 137 to the focal point 51, such that the laserbeam from both the first and second beam delivery paths 135, 137 arecoincident at the focal point 51. In FIG. 2, the laser beam from thesecond beam delivery path 137 is at an acute angle β with respect to thenormal 145 of the predefined plane 53. In this embodiment, due thesymmetry of the positions of the first and second focusing lenses 143,149, the angle β and the angle α are equivalent.

The laser system 111 includes a positioning assembly, which forsimplicity in FIG. 2 is depicted by the support structures 163, 165,167, 169. Although not shown explicitly, it should be understood thatthe positioning assembly, including the support structures 163, 165,167, 169, also includes one or more servo motors or other rotary/linearactuators, electronics, and other components which enable thepositioning assembly to move the various optical components as shown anddescribed. The positioning assembly, through the support structures 163,165, 167, 169, is configured to move the first and second focusinglenses 143, 149 and the second and third mirrors 141, 147. In certainembodiments, each of the second and third mirrors 141, 147 and therespective support structures 163, 167 may be a single unit in the formof a steering mirror or a fast steering mirror.

The laser system 111 also includes a controller 71 which is operablycoupled to the laser source 13, the detector 25, and each of the supportstructures 163, 165, 167, 169 through control lines to enable fullcontrol of the laser system 111, including positioning of the focalpoint 51 and operation of the laser source 13 so that the substrate 17can be modified. The controller 71 enables simultaneous control overeach of the support structures 163, 165, 167, 169 to ensure that thelaser beam from both the first and second beam delivery paths 135, 137coincide at the focal point 51. In certain embodiments, the controller71 may be pre-programmed to perform a desired modification to thesubstrate 17 so that the modification process can be automated. Incertain other embodiments, the controller 71 may be operated by a userto enable control of the modification process in real time.

The support structure 163 supports the second mirror 141 and enablesrotation of the second mirror 141 about a central point of thereflective surface of the second mirror 141. The support structure 165supports the first focusing lens 143 and enables translation of thefirst focusing lens 143 in two directions, the first direction beingtoward and away from the substrate along an optical axis of the firstfocusing lens 143, and the second direction being orthogonal to thefirst direction. The support structure 165 also enables rotation of thefirst focusing lens 143 about one or more axes orthogonal to the opticalaxis of the first focusing lens 143. In combination, by being able torotate the second mirror 141 and independently rotate and translate thefirst focusing lens 143, the laser beam from the first beam deliverypath 137 may be brought to focus at the focal point 51. This combinationof movement also enables the focal point 51, and also the predefinedplane 53, to be moved deeper into the substrate 17 or toward the surfaceof the substrate 17.

The support structure 167 supports the third mirror 147 and enablesrotation of the third mirror 147 about a central point of the reflectivesurface of the third mirror 147. The support structure 169 supports thesecond focusing lens 149 and enables translation of the second focusinglens 149 in two directions, the first direction being toward and awayfrom the substrate along an optical axis of the second focusing lens149, and the second direction being orthogonal to the first direction.The support structure 169 also enables rotation of the second focusinglens 149 about one or more axes orthogonal to the optical axis of thesecond focusing lens 149. In combination, by being able to rotate thethird mirror 147 and independently rotate and translate the secondfocusing lens 149, the laser beam from the second beam delivery path 137may be brought to focus at the focal point 151, so that the laser beamfrom each of the first and second beam delivery paths 135, 137 coincideat the focal point 51.

In certain embodiments, the laser delivery assembly 131 and the supportstructures 163, 165, 167, 169 may be incorporated into a handhelddevice. In such an embodiment, the controller 71 may control the depthof the focal point 51 within the substrate, while the user manuallycontrols lateral movement of the focal point 51 within the predefinedplane 53. Alternatively, in such an embodiment the user may operate thecontroller to set the focal point 51 at a fixed distance from the laserdelivery assembly 131, thereby requiring the user to manually controlthe depth of the focal point 51 within the substrate 17 while alsomanually controlling lateral movement of the focal point 51 within thepredefined plane 53.

In the embodiment shown, the beam delivery paths 135, 137 are shown ashaving different optical path lengths. In certain embodiments, arefractive beam splitter may be employed, instead of the reflective beamsplitter shown, in lieu of introducing a time delay into one of the beamdelivery paths. In certain other embodiments, additional opticalelements may be introduced into the shorter of the two paths so that thebeam delivery paths 135, 137 have the same optical path length.

In certain embodiments of the laser delivery assembly 131, additionalbeam delivery paths may be added by placement of the appropriate opticalcomponents. Any such additional beam delivery paths that are introducedinto the laser delivery assembly 131 may use any of the beam steeringand beam focusing techniques expressly or impliedly disclosed herein.Such additional delivery paths may have the same or different opticalpath lengths as compared to the beam delivery paths 135, 137.

FIG. 3 illustrates another embodiment of a laser system 211 which may beused to modify a substrate 17. The laser system 211 includes a lasersource 13 configured to generate a laser beam formed by a plurality ofultra-short pulses 15, and the laser beam is directed toward and intothe substrate 17. In certain embodiments, the laser source 13 may be afemtosecond laser. In certain embodiments, the laser source 13 maygenerate the laser beam in the infrared to near-infrared wavelengths. Incertain embodiments, the laser source 13 may be a tunable pulsed lasersource.

The laser beam is directed along a primary beam path 19, in which otheroptical elements of the laser system 211 are positioned to interact withthe laser beam. From the laser source 13, the laser beam is directedalong the primary beam path 19 to beam/pulse shaping optics 21, whichmay be used to manipulate the temporal profile of the ultra-short laserpulses. Again, depending upon the form of the ultra-short pulses 15produced by the laser source 13 and the application for which the lasersystem 211 is being used, in certain embodiments the beam/pulse shapingoptics 21 may be omitted from the laser system 211. In certainembodiments, the laser beam may pass through any number of lenses,polarizers, splitters, mirrors, and/or fibers after being generated bythe laser source and before entering the substrate. Such additionaloptical elements, although they may be present in certain embodiments,are not to be limiting of the invention unless expressly recited in theclaims.

Following the beam/pulse shaping optics 21, the laser beam is directedthrough a dichroic mirror 23, which allows the laser beam to passthrough and directs light emitted from excitation events into thedetector for feedback and analysis.

After passing through the dichroic mirror 23, the laser beam is directedto the laser delivery assembly 231, which is housed within thepositioning assembly 261. Within the laser delivery assembly 231, thelaser beam passes through a focusing mirror 239, after which the beamsplitter 233 splits the primary beam path 19 into a first beam deliverypath 235 and a second beam delivery path 237. The laser beam is thusalso divided between the first beam delivery path 235 and the secondbeam delivery path 237, in the same manner as previously described. Thefocusing mirror 239 focuses the laser beam passing along both the firstand second beam delivery paths 237, 237 at the focal point 51.

As shown, the beam splitter 233 uses reflection to split the laser beambetween the first and second beam delivery paths 235, 237. In certainembodiments, other types of reflective and/or refractive beam splittersmay also be used.

In order to achieve the desired coincidence at the focal point 51, theoptical path length of the first and second beam delivery paths 235,237, between the point of incidence of the primary beam path 19 with thebeam splitter 233 and the focal point 51, should be the same. Asdiscussed above, a time delay optical element may be incorporated intothe laser delivery assembly 231 as needed.

A first mirror 241 is in the first beam delivery path 235 immediatelyfollowing the beam splitter 233. This first mirror 239 is in a fixedposition and directs the laser beam along the first beam delivery path235 to a second mirror 243, which is also in a fixed position. Thesecond mirror 243 in turn directs the laser beam along the first beamdelivery path 235 to the focal point 51. In FIG. 3, the laser beam fromthe first beam delivery path 235 is at an acute angle α with respect tothe normal 247 of the predefined plane 53.

A third mirror 245 is in the second beam delivery path 237. The thirdmirror 245 is in a fixed position in order to direct the laser beamreflected from the beam splitter 233 along the second beam delivery path237 to the focal point 51, such that the laser beam from both the firstand second beam delivery paths 235, 237 are coincident at the focalpoint 51. In FIG. 3, the laser beam from the second beam delivery path237 is at an acute angle β with respect to the normal 145 of thepredefined plane 53. In this embodiment, due the symmetry of thepositions of the first and second mirrors 243, 245, the angle β and theangle α are equivalent.

The positioning assembly 261, which for simplicity in FIG. 2 is depictedby an enclosure, should be understood to also include one or more servomotors or other rotary/linear actuators, electronics, and othercomponents which enable the positioning assembly to move the laserdelivery assembly 231 as shown and described.

The laser system 211 also includes a controller 71 which is operablycoupled to the laser source 13, the detector 25, and the positioningassembly 261 through control lines to enable full control of the lasersystem 211, including positioning of the laser delivery assembly 231 andoperation of the laser source 13 so that the substrate 17 can bemodified. In certain embodiments, the controller 71 may bepre-programmed to perform a desired modification to the substrate 17 sothat the modification process can be automated. In certain otherembodiments, the controller 71 may be operated by a user to enablecontrol of the modification process in real time.

In certain embodiments, positioning assembly 261 may be incorporatedinto a handheld device. In such an embodiment, the controller 71 maycontrol the depth of the focal point 51 within the substrate, while theuser manually controls lateral movement of the focal point 51 within thepredefined plane 53. Alternatively, in such an embodiment the user mayoperate the controller to set the focal point 51 at a fixed distancefrom the laser delivery assembly 231, thereby requiring the user tomanually control the depth of the focal point 51 within the substrate 17while also manually controlling lateral movement of the focal point 51within the predefined plane 53.

In the embodiment shown, the beam delivery paths 35, 37 are shown ashaving different optical path lengths. In certain embodiments, arefractive beam splitter may be employed, instead of the reflective beamsplitter shown, in lieu of introducing a time delay into one of the beamdelivery paths. In certain other embodiments, additional opticalelements may be introduced into the shorter of the two paths so that thebeam delivery paths 235, 237 have the same optical path lengths.

In certain embodiments of the laser delivery assembly 231, additionalbeam delivery paths may be added by placement of the appropriate opticalcomponents. Any such additional beam delivery paths that are introducedinto the laser delivery assembly 231 may use any of the beam steeringand beam focusing techniques expressly or impliedly disclosed herein.Such additional delivery paths may have the same or different pathlengths as compared to the beam delivery paths 235, 237.

Each of the laser system embodiments described in connection with FIGS.1-3 allow for the delivery of electromagnetic radiation energy in onlyat the focal point where the laser beam from the multiple beam deliverypaths coincide. Moreover, the adjustability of the focal point withinthe substrate introduces significant versatility to the laser systemsand benefits for their use. In the field of medicine, particularly forthe treatment of tissue using the laser systems disclosed herein,benefits may be had over existing technologies, including one or moreof: (1) lower individual energies may be used along each beam deliverypath so that less adjacent tissue damage occurs; (2) the depth may becontrolled more accurately as the dispersion of energies is even lowerthan current technology so that the probability of multiphotonnon-linear excitement in an unwanted location within tissue is so lowthat it largely only occurs precisely at the focal point, which is thepoint of coincidence for the laser beam emerging from each of themultiple beam delivery paths; (3) the addition of more lenses canprovide finer control of energy delivery, thus allowing both coarse andfine adjustments; (4) the increased precision allows for the ability toisolate individual layers of the tissue, such as in skin, for treatment;(5) tissues at greater depths may be treated allowing for treatment ofnot just skin, but also subcutaneous tissues, fat, and blood vessels.

A flowchart 311 showing a process for delivering a laser beam havingultra-short pulses along multiple mean delivery paths is shown in FIG.4. The process of this flowchart 311 may be utilized with any of thelaser system embodiments disclosed herein. Alternatively, the process ofthis flowchart 311 may be utilized with any other appropriate lasersystem which is capable of performing the process steps as set forth inthe claims. Thus, the process steps are not to be limited to use withany particular laser system embodiment unless otherwise expresslyrecited in the claims. In the first step of the process, a laser beamhaving ultra-short pulses is generated 313. In certain embodiments, thelaser beam may be generated by a femtosecond laser. In certain otherembodiments, any laser or laser system capable of generating a series ofultra-short pulses may be used. In the following step, the generatedlaser beam is split 315 between multiple beam delivery paths. The numberof beam delivery paths may vary. The number of beam delivery paths maybe as few as two, or it may be any greater number of beam deliverypaths, limited only by the resources of the process user. In certainembodiments, it may be desirable to evenly distribute the pulse energyof the laser beam amongst the multiple beam delivery paths. In certainother embodiments, the pulse energy of the laser beam may be unevenlydistributed amongst the multiple delivery paths, with one or more of thebeam delivery paths receiving a greater amount of pulse energy than theother beam delivery paths. In most embodiments, the distribution pulseenergy is largely determined by the choice and specifications of thebeam splitter. In the next step, the laser beam from each delivery pathis focused 317 to a common focal point. By focusing the laser beam fromeach delivery path to a common focal point, the pulse energy that waspreviously distributed between the multiple delivery paths is made to becoincident at the focal point, so that the now recombined pulse energymay induce a multiphoton excitation event, while the laser beam fromeach individual beam delivery path does not include enough pulse energyto induce a multiphoton excitation event. In certain embodiments, thefocusing step 317 may be performed before the splitting step 315, withthe result being that the pulse energy from each delivery path is stillmade to be coincident at a common focal point.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques. It is tobe understood that other embodiments may be utilized and structural andfunctional modifications may be made without departing from the scope ofthe present invention. Thus, the spirit and scope of the inventionshould be construed broadly as set forth in the appended claims.

What is claimed is:
 1. A laser system comprising: a laser sourcegenerating a laser beam comprising ultra-short pulses; a laser deliveryassembly optically coupled to the laser source to receive the laserbeam, the laser delivery assembly comprising: a beam splitter configuredto split the laser beam between a first beam delivery path and a secondbeam delivery path; and at least one focusing lens optically coupled tothe beam splitter and configured to focus the laser beam from each ofthe first beam delivery path and the second beam delivery path to afocal point on a predefined plane; wherein the first beam delivery pathintersects the predefined plane at a first angle, the second beamdelivery path intersects the predefined plane at a second angle, and afirst pulse from the first beam delivery path and a second pulse fromthe second beam delivery path are coincident at the focal point toenable creation of a multiphoton non-linear excitation at the focalpoint, the focal point being on a specific layer of a target substrate.2. The laser system of claim 1, wherein the second angle is differentfrom the first angle.
 3. The laser system of claim 1, wherein the secondangle is equivalent to the first angle.
 4. The laser system of claim 1,wherein the first beam delivery path and the second beam delivery pathhave different path lengths.
 5. The laser system of claim 1, wherein theat least one focusing lens is in a path of the laser beam before thebeam splitter.
 6. The laser system of claim 1, wherein the beam splitteris in a path of the laser beam before the at least one focusing lens. 7.The laser system of claim 1, further comprising a positioning assembly,the laser delivery assembly coupled to the positioning assembly, whereinthe positioning assembly is configured to move at least one of the laserdelivery assembly and the at least one focusing lens.
 8. The lasersystem of claim 7, wherein the positioning assembly is configured tomove the laser delivery assembly using at least one of translation androtation.
 9. The laser system of claim 7, wherein the positioningassembly is configured to move the at least one focusing lens using atleast one of translation and rotation.
 10. The laser system of claim 7,the laser delivery assembly further comprising at least one mirroroptically coupled to the at least one focusing lens, wherein thepositioning assembly is configured to rotate the at least one mirror.11. A method of modifying a substrate, the method comprising: generatinga laser beam comprising ultra-short pulses; splitting the laser beambetween a first beam delivery path and a second beam delivery path;focusing the laser beam from each of the first beam delivery path andthe second beam delivery path to a focal point on a predefined planewithin the substrate, the first beam delivery path intersecting thepredefined plane at a first angle, and the second beam delivery pathintersecting the predefined plane at a second angle, wherein a firstpulse from the first beam delivery path and a second pulse from thesecond beam delivery path are coincident at the focal point, the focalpoint being on a specific layer of the substrate; and creating amultiphoton non-linear excitation at the focal point.
 12. The method ofclaim 11, wherein the second angle is different from the first angle.13. The method of claim 11, wherein the second angle is equivalent tothe first angle.
 14. The method of claim 11, wherein focusing the laserbeam is performed before splitting the laser beam.
 15. The method ofclaim 11, wherein splitting the laser beam is performed before focusingthe laser beam.
 16. The method of claim 15, wherein focusing the laserbeam comprises: focusing the laser beam from the first beam deliverypath to the focal point using a first focusing lens disposed in thefirst beam delivery path; and focusing the laser beam from the secondbeam delivery path to the focal point using a first focusing lensdisposed in the first beam delivery path.
 17. The method of claim 11,further comprising: moving at least one of the focal point within thepredefined plane and the predefined plane by moving each of the firstfocusing lens and the second focusing lens.
 18. The method of claim 17,wherein moving at least one of the focal point within the predefinedplane and the predefined plane comprises at least one of translating androtating at least one of the first focusing lens and the second focusinglens.
 19. The method of claim 17, wherein moving at least one of thefocal point within the predefined plane and the predefined planecomprises rotating at least one mirror optically coupled to one of thefirst focusing lens and the second focusing lens.
 20. A laser systemcomprising: a laser source generating a laser beam comprisingfemtosecond pulses; a laser delivery assembly optically coupled to thelaser source to receive the laser beam, the laser delivery assemblycomprising: a beam splitter configured to split the laser beam between afirst beam delivery path and a second beam delivery path; a firstfocusing lens optically coupled to the beam splitter and positionedwithin the first beam delivery path, the first focusing lens configuredto focus the laser beam from the first beam delivery path to a focalpoint on a predefined plane; a second focusing lens optically coupled tothe beam splitter and positioned within the second beam delivery path,the second focusing lens configured to focus the laser beam from thesecond beam delivery path to the focal point on the predefined plane;wherein the first beam delivery path intersects the predefined plane ata first angle, the second beam delivery path intersects the predefinedplane at a second angle, and a first pulse from the first beam deliverypath and a second pulse from the second beam delivery path arecoincident at the focal point to enable creation of a multiphotonnon-linear excitation at the focal point, the focal point being on aspecific layer of a target substrate.